This four-year project will be carried out by Abt Associates, the Guangxi Center for HIV/AIDS Prevention and Control, the National AIDS Standing Bureau of Vietnam, and Beth Israel Medical Center in New York City. This will be the first ever intervention designed to prevent cross-border HIV transmission. It will target Ning Ming County, Guangxi Province, China and Langson Province, Vietnam, a border area seriously affected by large-scale drug trafficking and cross-border movement related to small-scale drug purchase and use, an HIV epidemic that appears poised to enter a take-off stage, and very limited HIV prevention activities to date. The intervention will be a comprehensive, peer education model embracing elements of social marketing, risk reduction for drug users, public health infection control, and community education. It will be evaluated through repeat cross-sectional behavioral surveys and measurement of cross-sectional HIV seroprevalence, with a "capture-recapture" component allowing analysis of longitudinal behavior change and estimation of HIV incidence. Community KAP surveys and peer educators' process data will be employed as well. The project also seeks to improve cross-border collaboration on and in-country capacity for prevention interventions, positive policy development, and behavioral and epidemiologic research. This intervention is considered as a "structural" intervention with assessment at the community level. The specific aims are as follows: 1) Show control of HIV transmission on both sides of the border through stable HIV prevalence rates among IDUs (currently -10 percent); 2) Show control of HIV transmission on both sides of the border by low HIV incidence (targeting 1/100 person-years at hisk) among IDUs; 3) Show very large reductions in HIV injection risk behavior, from the currently estimated 60 percent of IDUs engaging in receptive sharing of needles and syringes to a stable level of 30 percent; 4) Show large reductions in HIV transmission behavior, from the currently estimated 60 percent of IDUs engaging in distributive sharing to a stable level of 30 percent; 5) Show statistically significant reductions in unsafe sexual behavior among IDUs; 6) Demonstrate very-large scale safe disposal of used injection equipment, with a target safe disposal of 150,000 used syringes per year; 7) achieve significant increases in HIV knowledge and in expressed support for the project interventions among samples of residents in the target communities.